import java.util.LinkedList;
import java.util.Queue;

class MyStack {
    private Queue<Integer>qu1;
    private Queue<Integer>qu2;
    public MyStack() {
        qu1=new LinkedList<>();
        qu2=new LinkedList<>();
    }
    
    public void push(int x) {
        if(!qu1.isEmpty()){
            qu1.offer(x);
        } else if(!qu2.isEmpty()){
            qu2.offer(x);
        }else {
            qu1.offer(x);
        }
    }
    
    public int pop() {
        //出栈
        if(empty()){
            return -1;
        }
        if(!qu1.isEmpty()){
            int size=qu1.size();
            for (int i = 0; i < size-1; i++) {
                qu2.offer(qu1.poll());
            }
            return qu1.poll();
        }else{
            int size=qu2.size();
            for (int i = 0; i < size-1; i++) {
                qu1.offer(qu2.poll());
            }
            return qu2.poll();
        }
    }
    
    public int top() {
        if(empty()){
            return -1;
        }
        if(!qu1.isEmpty()){
            int size=qu1.size();
            int ret=-1;
            for (int i = 0; i < size; i++) {
                ret=qu1.poll();
                qu2.offer(ret);
            }
            return ret;
        }else{
            int size=qu2.size();
            int ret=-1;
            for (int i = 0; i < size; i++) {
                ret=qu2.poll();
                qu1.offer(ret);
            }
            return ret;
        }
    }
    
    public boolean empty() {
        return qu1.isEmpty()&&qu2.isEmpty();
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */